Most oil and gas well logs are available only on microfiche or microfilm in analog form and are not readily available in digital form. While there has been some capturing of well logs in digital form during about the past 15 years, most well logs are still not digitized. The benefit of digitized well logs is that they are easily processed using commonly available general purpose computers already in use in the industry.
There are currently under development devices that are intended to rasterize images of complete microfiche and store them on optical disc for subsequent access. However, it is not believed that this approach will meet the needs of the oil and gas servicing industry for a convenient, low cost, interactive interface between a general purpose computer and the data residing in microfiche well log libraries.
In general, image acquisition devices can be classified into two categories, depending on whether the size of the image to be captured can be projected at the required resolution onto the active sensor area or not. This invention is concerned with the category where the size of the image at the required resolution is larger then the active area of the sensor. This requires a means of controlled movement of the image pass the field of view of the sensor. One method of doing this is to move the image to be acquired with a precision transport device 1 pixel at a time into the field of view of the sensor. The acquired image is the mosaic of successive image separated by the known spatial separation determined by the movement of the transport device. Another method of doing this is to move the image to be acquired or a reflected image from a mirror system at a constant speed past the field of view of the sensor. The acquired image is a mosaic of successive images separated by a spatial separation derived from the image acquisition rate and the velocity at which the image is moved pass the field of view of the sensor.
Both of the above techniques require a mechanical coupling of the image to be acquired to the image acquisition device. The quality and ultimate resolution of the image will be determined by the tolerance of this mechanical coupling, the distance moved or the ability to maintain a constant velocity. Since microfiche is moved by hand in the XY plane, it will be appreciated that precision of the mechanical coupling is quite difficult to achieve.
The inventors have proposed a new method and apparatus for capturing a digital representation ("image") of data contained in the XY plane such as a microfiche well log that does not rely on mechanical coupling of the microfiche log to the image acquisition device.
In the operation of the present invention, sensors, preferably solid state sensors, are used to capture (acquire and store) in digital form a series of optical images of the two dimensional data. Information in the series of optical images themselves is used to detect the motion of the images. To do this, a subject (current) digitized image is compared with a saved (reference) digitized reference image. The correlation function of the subject image with respect to the reference image is used to calculate the motion of the image in order to determine whether any particular captured image is to be stored in a permanent fashion and to assign location parameters to it.
In one aspect of the invention, therefore, the apparatus, which would be attached to a microfiche reader, would sense and measure image motion and provide a rasterized image to a general purpose computer for subsequent processing.
This invention does not require the image to be moved by some precise mechanical means past the field of view of the sensor. Without the need for any mechanical coupling, the ultimate resolution that can be achieved is only limited by the optics of the device. The technique used for image acquisition is applicable for arbitrary image motion (subject to a maximum velocity) in two dimensions.
In the case where the microfiche record or object being digitized lacks optical features that are resolvable by the sensors, that is, where the image is sparse, it is necessary to use some means to ensure that the image is non-sparse. This may be achieved, for example, by superimposing a grid on the microfiche or attaching some other non-sparse device to the microfiche carrier. This non-sparse device may then be imaged by an area sensor to carry out motion detection in accordance with the principles of the invention. At the same time, the microfiche record is imaged preferably using some other sensor such as a linear sensor and the record may be reconstructed using the image acquired using the linear sensor and an indication of the degree of motion of the non-sparse device.